1. Field of the Invention
The present invention relates to a resin coated optical fiber for an optical fiber cord, the resin coated optical fiber having superior connector insertion characteristics and low temperature characteristics when the resin coated optical fiber is used for an optical fiber cord.
2. Description of Related Art
As a resin coated optical fiber used for an optical fiber cord, conventionally, a resin coated optical fiber formed by coating a coating layer formed of a thermoplastic resin such as nylon 12 around a reinforcing resin coated optical fiber having an outer diameter of 0.4 to 0.5 mm so that the resin coated optical fiber has an outer diameter of 0.9 mm, is used. The reinforcing resin coated optical fiber is formed by coating a reinforcing layer such as silicone resin, UV curable resin, or the like, around a bare optical fiber having an outer diameter of 125 xcexcm.
The above resin coated optical fiber, in particular, a thermoplastic resin coated optical fiber is formed to an optical fiber cord by longitudinally providing a tensile fiber composed of an aramid fiber and the like along the thermoplastic resin coated optical fiber, and providing an outer jacket composed of a resin such as polyvinyl chloride, nylon, or the like.
When one optical fiber cord is connected to another optical fiber cord, a connector is generally used. Various connectors having different structures are known. Among these, an xe2x80x9cSC connectorxe2x80x9d will be explained as an example.
An SC connector is generally composed of two plugs which respectively fix one end of the first optical fiber cord and one end of the second optical fiber cord, which the cords are connected to each other, and an adaptor for engaging both plugs.
FIGS. 5A to 5C are schematic views of a state in which the end of the optical fiber cord is engaged in the plug of the above-described SC connector. Optical fiber cord 10 and plug 30 are shown in FIGS. 5A to 5C.
Plug 30 is composed of plug frame 32, spring 33, stop ring 34, caulking ring 35, caulking ring 36, rubber hood 37, and housing 38.
Outer jacket 12 and tensile fiber 14 of optical fiber cord 10 are peeled a predetermined length from the end of optical fiber cord 10, so that the predetermined distance of thermoplastic resin coated optical fiber 16 is exposed. Furthermore, tensile fiber 14 is pressed and closely fitted using caulking ring 35 and the outer jacket 12 is pressed and closely fitted using caulking ring 36.
In thermoplastic resin coated optical fiber 16, the reinforcing layer and the coating layer are peeled a predetermined length from the end (not shown) so as to expose the bare optical fiber, and the bare optical fiber is inserted into ferrule 20. Furthermore, receiving member 21 is provided around ferrule 20. Receiving member 21 is provided between ferrule 20 and stop ring 34. Spring 33 for pushing ferrule 20 toward the connection part of the connector to be connected the other connector is received by receiving member 21.
When the connector is not engaged to the other connector, as shown in FIG. 5A, the end surface 22 of ferrule 20 is pushed by spring 33 toward the connection part of the connector to be connected the other connecter, so that a predetermined length of the end portion of ferrule 20 protrudes from housing 38.
Furthermore, when the connector is engaged to the other connector, as shown in FIG. 5B, the end surface 22 of ferrule 20 (i.e., the first ferrule of the first plug) is pushed by the end surface of the second ferrule of the second plug (not shown) and is pushed toward an insertion port of plug 30. Then, spring 33 is contracted by receiving member 21, and the end surfaces of the first and second ferrules are pushed and closely contacted with each other by elasticity of spring 33, so that the connectors are satisfactorily engaged and this state is maintained. The length of ferrule 20 pushed toward the insertion port of plug 30 when the connectors are engaged is normally approximately 0.5 mm.
When the first and second optical fiber cords are connected to the connectors as described above, if thermoplastic resin coated optical fiber 16 has low flexural rigidity, as shown in FIG. 5C, ferrule 20 is pushed and subsequently thermoplastic resin coated optical fiber 16, which is placed behind ferrule 20, is bent. As a result, loss increases. In order to prevent thermoplastic resin coated optical fiber 16 from bending, flexural rigidity of the thermoplastic resin coated optical fiber used for the optical fiber cord is generally determined to be 18 to 25 Nxc2x7mm2.
In recent years, in order to actualize high speed drawing of the optical fiber and to improve productivity, as the above-described reinforcing resin coated optical fiber having an outer diameter of 0.25 mm is generally used. The reinforcing resin coated optical fiber is formed by coating the bare optical fiber with the reinforcing layer composed of a UV curable resin which can make the reinforcing layer thin and fast curing.
When the above reinforcing resin coated optical fiber having small diameter is used for the thermoplastic resin coated optical fiber having an outer diameter of 0.9 mm, there are some problems as follows.
(1) The thickness of the coating layer becomes thick. When the thremoplastic resin coated optical fiber is exposed to low temperatures, the amount of shrinkage of the coating layer increases. Accordingly, a slight bend is generated in the optical fiber, and then, loss increases.
(2) If a soft material is used for the coating layer of the thermoplastic resin coated optical fiber in order to prevent variation of loss under low temperatures, when the optical fiber cord manufactured from the thermoplastic resin coated optical fiber made by using the soft material is connected to the other optical fiber cord with the connector as described above, the peeled part of thermoplastic resin coated optical fiber 16 placed behind ferrule 20, tends to bend as shown in FIG. 5C, and therefore, loss may increase.
In light of the above problems, an object of the present invention is to provide a thermoplastic resin coated optical fiber which prevents loss from increasing when the optical fiber cord is connected to another optical fiber cord using a connector or when exposed to low temperatures, and exhibits superior transmission characteristics, even if a reinforcing resin coated optical fiber having the outer diameter of 0.25 mm is used as a starting material for the thermoplastic resin coated optical fiber for an optical fiber cord.
The above object is solved by the following aspect of the present invention.
An aspect of the present invention is that a thermoplastic resin coated optical fiber having an outer diameter of 0.81 to 0.99 mm, comprising a reinforcing resin coated optical fiber having an outer diameter of 0.225 to 0.275 mm, wherein a coating layer is provided around the reinforcing resin coated optical fiber, and a flexural rigidity of the thermoplastic resin coated optical fiber is 5.5 to 7.5 Nxc2x7mm2.
According to the above aspect, an optical fiber cord obtained by sequentially providing a tensile fiber and the outer jacket around the thermoplastic resin coated optical fiber prevents loss from increasing when two optical fiber cords are connected to each other using a connector. Furthermore, loss is prevented from increasing under low temperatures.
Furthermore, according to the above aspect, the thermoplastic resin coated optical fiber has sufficient transmission characteristics. At the same time, the outer diameter of the reinforcing resin coated optical fiber used for the thermoplastic resin coated optical fiber is more slender than that of a conventional optical fiber, and is formed by high-speed drawing, and therefore, productivity of the thermoplastic resin coated optical fiber is improved.
The coating layer may comprise a thermoplastic resin having a bending elastic modulus of 200 to 350 MPa. Accordingly, the flexural rigidity of the thermoplastic resin coated optical fiber is maintained within 5.5 to 7.5 Nxc2x7mm2.
Furthermore, polyester elastomer may be used as the thermoplastic resin.
The outer diameter of the reinforcing resin coated optical fiber generally has a dispersion of xc2x110% to the standard values through manufacturing processes, and similarly, the outer diameter of the thermoplastic resin coated optical fiber has a dispersion of xc2x110% to the standard values. Accordingly, in the reinforcing resin coated optical fiber and the thermoplastic resin coated optical fiber of the present invention, these outer diameters are usually 0.25 mm and 0.9 mm respectively, but these have dispersions of xc2x110%. The outer diameter of the reinforcing resin coatd optical fiber is 0.225 to 0.275 mm and the outer diameter of the thermoplastic resin coated optical fiber is 0.81 to 0.99 mm.